Cellular wireless communication systems support wireless communication services in many populated areas of the world. While cellular wireless communication systems were initially constructed to service voice communications, they are now called upon to support data communications as well. The demand for data communication services has exploded with the acceptance and widespread use of the Internet. While data communications have historically been serviced via wired connections, cellular wireless users now demand that their wireless units also support data communications. Many wireless subscribers now expect to be able to “surf” the Internet, access their email, and perform other data communication activities using their cellular phones, wireless personal data assistants, wirelessly linked notebook computers, and/or other wireless devices. The demand for wireless communication system data communications continues to increase with time. Thus, existing wireless communication systems are currently being created/modified to service these burgeoning data communication demands.
Cellular wireless networks include a “network infrastructure” that wirelessly communicates with wireless terminals within a respective service coverage area. The network infrastructure typically includes a plurality of base stations dispersed throughout the service coverage area, each of which supports wireless communications within a respective cell (or set of sectors). The base stations couple to base station controllers (BSCs), with each BSC serving a plurality of base stations. Each BSC couples to a mobile switching center (MSC). Each BSC also typically directly or indirectly couples to the Internet.
In operation, each base station communicates with a plurality of wireless terminals operating in its cell/sectors. A BSC coupled to the base station routes voice communications between the MSC and the serving base station. The MSC routes the voice communication to another MSC or to the PSTN. BSCs route data communications between a servicing base station and a packet data network that may include or couple to the Internet. Transmissions from base stations to wireless terminals are referred to as “forward link” transmissions while transmissions from wireless terminals to base stations are referred to as “reverse link” transmissions.
Wireless links between base stations and their serviced wireless terminals typically operate according to one (or more) of a plurality of operating standards. These operating standards define the manner in which the wireless link may be allocated, setup, serviced, and torn down. One popular cellular standard is the Global System for Mobile telecommunications (GSM) standard. The GSM standard, or simply GSM, is predominant in Europe and is in use around the globe. While GSM originally serviced only voice communications, it has been modified to also service data communications. GSM General Packet Radio Service (GPRS) operations and the Enhanced Data rates for GSM (or Global) Evolution (EDGE) operations coexist with GSM by sharing the channel bandwidth, slot structure, and slot timing of the GSM standard. The GPRS operations and the EDGE operations may also serve as migration paths for other standards as well, e.g., IS-136 and Pacific Digital Cellular (PDC).
Many different communication channels are available. Communications channels allow wired or wireless communications for the transmission of audio, video and data. These wired, wireless and optical communication channels may include fiber optics, laser based communications, satellite based communications, cellular communications, cable communications, radio frequency (RF) and traditional wired and wireless communications. These communications allow for the delivery of video, Internet, audio, voice, and data transmission services throughout the world. By providing communication channels with large bandwidth capacity, communications channels facilitate the exchange of information between people in an ever shrinking global environment.
As the amount of data exchanged increases, the ability to accurately read data from the channels is adversely effected. One factor affecting the ability to accurately read this data is inter symbol interference (ISI). ISI is the process by which nearby symbols interact with each other in a detrimental way. To allow higher data exchanges within a physical channel, one solution in telecommunications and data storage has been to intentionally write symbols close together and utilize the Viterbi algorithm (or any other sequence detector) and knowledge of how the symbols interact to recover the bit sequence from a noisy analog signal. When applying this solution, the data interferes in a controlled manner and additionally becomes distorted by noise and/or other interfering signals. This noise and interfering signals must be overcome in order to properly read back the pattern of “1's” and “0's” correctly. The Viterbi algorithm is an efficient dynamic programming algorithm that finds the most likely sequence of bits received by comparing a received sequence of points sampled from the analog read back waveform to every possible sequence of bits transmitted. This best sequence is referred to as the “best path through the trellis.” The trellis tracks all possible paths and consists of states, which help track the bit decisions associated with the path through them. Other techniques design symbols that are more robust against ISI. Decreasing the symbol rate (the “baud rate”), and keeping the data bit rate constant (by coding more bits per symbol), reduces inter symbol interference.
Thus, a need exists for improvements in interference cancellation.